This invention relates to voltage controlled oscillators, and more particularly, to voltage controlled oscillators that include tunable dielectric devices.
Communication systems are in need of low phase noise, high frequency, higher power and low cost voltage controlled oscillators (VCOs) for use in transmit/receive modules. VCOs are typically used for local oscillators to perform frequency up or down conversions. At higher frequencies, the phase noise of a local oscillator becomes increasingly important for recovering base band signals with minimized distortions. A high performance voltage controlled oscillator (VCO) requires resonant components to be high in Q value.
VCOs utilizing mechanically tuned dielectric resonators are known in the art. Examples of such VCOs can be found in U.S. Pat. Nos. 4,639,690 and 5,578,969. Diode varactors have been used in VCOs at lower frequencies. Examples of such VCOs can be found in U.S. Pat. Nos. 5,233,319 and 5,982,244. However, at microwave frequencies diode varactors become lossy and introduce noise.
While various voltage controlled oscillator topologies are known in the art, there remains a need to provide VCOs that can operate at high frequencies and provide both lower phase noise and wider tuning bandwidth. This invention seeks to fulfill that need.
Voltage controlled oscillators constructed in accordance with this invention include an active element having a first connection point for connection to a voltage source and an output connection point. A tunable resonator including a first voltage tunable dielectric device is connected to an input of the active element. A first circuit branch is also connected to the active element. A control voltage is applied to the voltage tunable dielectric device to control the frequency of an oscillating voltage at the output connection point. In a reflect type voltage controlled oscillator, the first circuit branch is a bypass circuit. In a transmission type voltage controlled oscillator, the first circuit branch includes a phase shifter and is connected between the active element output connection point and the tunable resonator.
The first circuit branch can include a second voltage tunable dielectric device, in which case a control voltage can also be applied to the second voltage tunable dielectric device to control the frequency of an oscillating voltage at the output connection point.
The voltage controlled oscillators of this invention can include a high Q resonant circuit that provides both improved low phase noise and wide tuning bandwidth. These VCOs can operate in high power applications, while employing a low cost, high Q, linear dielectric tunable capacitor or a low loss phase shifter with effectively no power consumption. These VCOs typically have a phase noise of less than xe2x88x9275 dBc/Hz at 10 KHz offset from microwave carrier frequency and a tuning bandwidth of up to 50%. The tunable components can be fabricated or printed on a single substrate or integrated in a single device.
These and other features and advantages of the present invention will become apparent in the following detailed description of illustrative embodiments thereof, which is to be read in connection with the accompanying drawings.